Abstract: A 15-week feeding trial was conducted to study the effects of dietary potassium on growth and physiological responses of juvenile abalone, Haliotis discus hannaiIno. Six casein-gelatin based semi-purified diets containing graded levels of dietary potassium (KCl, 0.10, 2.12, 4.39, 9.79, 20.08 and 27.26 g/kg dry diet, respectively) were fed to juvenile abalone initial weight: (0.24 0.00) g; initial shell length: (12.24 0.04) mm in triplicate groups in a flow-through system. During the experimental period, the water temperature ranged from 12 to 23℃ and potassium concentration was (472.94 3.59) mg/L in the seawater. The results showed that there were no significant (P 0.05) differences in the weight gain ratio (WGR, %), daily increment in shell length (DISL, m/d) and the survival of abalone among treatments. There were also no significant (P 0.05) differences in lipid, moisture contents in soft body and ash content in shell among the six dietary treatments. Compared with that in the treatment of 0.10 g/kg diet, the protein content in soft body increased significantly (P 0.05) when dietary potassium was more than 4.39 g/kg diet. The content of potassium in the soft body and potassium, sodium in the shell was maintained relatively constant regardless of dietary treatment. The soft body sodium content was significantly (P 0.05) lower in 20.08 and 27.26 g/kg of dietary treatment than any other treatments. The activity of gill Na+-K+ ATPase decreased steadily with the increasing of dietary potassium. Data from the growth parameters (WGR and DISL) showed that it was unnecessary to add potassium to the diets, and the potassium from diet sources and seawater was sufficient for the optimal growth of juvenile abalone. Based on the physical index (protein and sodium contents in soft body and Na+-K+ ATPase activity in gill), the optimal concentration of dietary potassium was 2.12 g/kg.